Lubricating oil composition

ABSTRACT

The present invention aims to provide a lubricating oil composition capable of use in for example the bearings of a high-speed main shaft having ceramics ball antifrication bearings operating under severe conditions of high speed and high load. 
     To this end the present invention provides a lubricating oil composition, in particular for lubrication of ceramics, comprising a base oil; and at least one additive selected from the group consisting of: (i) an acid amide obtainable by reacting an amine with a saturated monocarboxylic acid having from 12 to 30 carbons or an unsaturated monocarboxylic acid having from 18 to 24 carbons; (ii) sarcosinic acid; and (iii) an aspartic acid derivative.

The present invention relates to a lubricating oil composition and in particular to a lubricating oil composition for lubrication of ceramics.

In recent years, for the purpose of not only responding to requests of users but also of achieving differentiation, Japanese machine tool manufacturers have aimed to realize high performance and high functionality. In particular, in machining centres (MC), machine tools capable of achieving working with high precision at a higher speed are being developed. Since 1982 in which machine tools capable of achieving a main shaft speed of 10,000 m⁻¹ first appeared, higher speed MC are being achieved every year, and recently, middle- or large-sized MC capable of achieving a main shaft speed exceeding 30,000 m⁻¹ have been put into practice. As technologies contributing to such realization of high speed, there may be mentioned oil-air lubrication, ceramics balls, and low exothermic robust bearings

In high-speed cutting work, the heat load on an antifriction bearing considerably increases, and the generation of scoring or scuffing becomes a problem. Therefore, oil-air lubricating oils which are used for such applications are strongly required to have low exothermicity and abrasion resistance or extreme pressure resistance.

Against such a background, as such lubricating oils, lubricating oils have hitherto been known in which an antioxidant, a rustproofing agent and a mild abrasion resistant agent are blended with a prescribed base oil.

However, even such lubricating oils do not yet confer sufficient benefits. See JP-A No. 5-320679.

As described above, it could not always be said that when a conventional lubricating oil is used for lubrication of a high-speed main shaft having a ceramics ball antifriction bearing, sufficient cooling performance and abrasion resistance or extreme pressure resistance of the bearing were achieved. That is, for applications in which excellent cooling properties, high extreme pressure resistance, abrasion resistance and rustproofing properties are required, lubricating oils to which a phosphorus-based extreme pressure agent such as trialkyl phosphoric acid esters or a sulphur-phosphorus based extreme pressure agent such as alkylated thiophosphates, Ca sulfonate or Ba sulfonate as a rustproofing agent, and the like are added are widely used. However, since the rustproofing agent has high adsorptivity to metal surfaces in view of its nature, there is a strong possibility that it may hinder the action of various extreme pressure agents of improving lubricating performance, and it is very difficult to make rustproofing properties and extreme pressure resistance coexist with each other.

In particular, in applications in which a lubricant is used at high temperature, even if the addition amount of the sulphur/phosphorus based extreme pressure agent is only a trace amount, when heat load is applied, a large quantity of sludge tends to be formed, thereby lowering cooling properties of the bearing. For that reason, with lubricating oils to which a sulphur based extreme pressure agent is added, it is difficult to obtain sufficient cooling properties and sludge resistant performance in a high-speed main shaft bearing having a ceramics ball antifriction bearing as described above.

On the other hand, although a phosphorus-based extreme pressure agent tends hardly to form sludge compared with a sulphur-based extreme pressure agent, when the phosphorus-based extreme pressure agent is used alone, it is difficult to obtain high-level cooling properties and extreme pressure resistance such as are required in lubricating oil for the high-speed main shaft of a ceramics ball antifriction bearing as aforesaid.

The present invention was made in view of these circumstances and aims to provide an excellent lubricating oil composition which even when used for a high-speed main shaft of a machine tool having a ceramics ball antifriction bearing which is operated under severe conditions of high speed and high load, exhibits sufficient cooling properties and has high rustproofing properties, high-level thermal oxidation stability and high extreme pressure resistance.

As a result of meticulous studies aimed at solving the above problem, the present inventors arrived at a lubricating oil composition, comprising a base oil; and at least one additive selected from the group consisting of: (i) an acid amide obtainable by reacting an amine with a saturated mono carboxylic acid having from 12 to 30 carbons or an unsaturated mono carboxylic acid having from 18 to 24 carbons; (ii) sarcosinic acid; and (iii) an aspartic acid derivative.

In addition, a lubricating oil composition of excellent lubrication properties between ceramics/iron or steel and excellent rustproofing properties can be obtained by employing in combination therewith at least one type selected from: a phosphorus-containing carboxylic acid, a phosphorus-containing carboxylic acid ester, an acidic phosphoric acid ester, an amine salt of an acidic phosphoric acid ester, a phosphorous acid ester, a phosphorothionate, a thiophosphoric acid ester, a thiophosphoric acid metal salt, a thiocarbamic acid ester, or a thiocarbamic acid metal salt.

Also, a lubricating oil composition having a sufficiently long oxidation life can be obtained by further addition of an aromatic amine compound or phenol-based compound.

With the lubricating oil composition according to the present invention, excellent low abrasion characteristics and cooling performance (ability to suppress rise in oil temperature) can be obtained even when used with for example a high-speed main shaft of a machine tool having a ceramics antifriction bearing used for machining under severe conditions in terms of high temperature and load. Also, the lubricating oil shows sufficiently long oxidation life, while maintaining a high level of abrasion resistance and extreme pressure performance. Consequently, the lubricating oil composition of the present invention is extremely useful in achieving suppression of generation of heat by a high-speed main shaft of a machine tool having ceramics ball antifriction bearings, and hence in achieving high precision machining by stabilisation of thermal displacement of the machine tool.

Preferred embodiments of the present invention are described in detail below. It should be noted that, in the following description, in cases where a compound or functional group may have either a straight chain structure or branch structure, both the straight chain structure and branch structure of the compound in question may be employed, unless otherwise specially noted.

The lubricating oil composition according to the present invention contains at least one type of base oil selected from mineral oil or synthetic oil.

As mineral oils, there may be mentioned by way of example paraffin type oils obtained by purification using a suitable combination of purification treatments such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, contact dewaxing, hydrofining, sulphuric acid washing, or platinum treatment of the lubricating oil fraction obtained by normal pressure distillation or reduced pressure distillation of crude oil.

As the base oil of these lubricating oil compositions, mineral oil, called highly refined base oil, or synthetic oil may be employed: in particular, base oil in the base oil category of the API (American Petroleum Institute) belonging to group I, group II, group III, group IV or group V, etc. may be employed, either alone or as a mixture.

The base oil that is herein employed may be of total sulphur no more than 1 weight %, preferably no more than 500 weight ppm, more preferably no more than 300 weight ppm, and even more preferably no more than 50 weight ppm. Also, its density at 15° C. may be 0.8 to 0.9, preferably 0.8 to 0.865 g/cm³, and even more preferably 0.81 to 0.84 g/cm³. The aromatic content may be less than 3%, preferably less than 2%, and even more preferably less than 0.1%.

Group I base oil includes for example paraffin-type mineral oil obtained by suitable combination of refining means such as solvent dewaxing of the lubricating oil fraction obtained by reduced pressure distillation of crude oil.

Group II base oil includes for example paraffin-type mineral oil obtained by suitable combination of refining means such as hydrocracking and dewaxing of the lubricating oil fraction obtained by normal pressure distillation of crude oil. Group II base oil refined by for example Gulf Oil's hydrofining method has total sulphur of less than 10 ppm and aromatics less than 5% and is ideal in the present invention. There is no particular restriction regarding the viscosity of such base oil and the viscosity index may be 80 to 120, preferably 100 to 120. The kinetic viscosity at 40° C. is preferably 2 to 680 mm²/s and even more preferably 8 to 220 mm²/s. Also the total sulphur may be less than 300 ppm, preferably less than 200 ppm, and even more preferably less than 10 ppm. The total nitrogen may be less than 10 ppm, preferably less than 1 ppm. In addition, the aniline point may be 80 to 150° C., preferably 100 to 135° C.

As the group III base oil and group II+ base oil there may suitably be employed for example paraffin-type mineral oil manufactured by a high degree of hydrofining of the lubricating oil fraction obtained by normal pressure distillation of crude oil or base oil generated by a dewaxing process, involving refining by the ISODEWAX process, in which dewaxing is performed by converting wax to isoparaffins, or base oil refined by Mobil's wax isomerization process.

There is no particular restriction regarding the viscosity of such base oils, but the viscosity index may be 95 to 145, preferably 100 to 140. The kinetic viscosity at 40° C. is preferably 2 to 680 mm²/s and even more preferably 8 to 220 mm²/s. Also the total sulphur may be 0 to 100 ppm, preferably less than 10 ppm. The total nitrogen may be less than 10 ppm, preferably less than 1 ppm. In addition, the aniline point may be 80 to 150° C., preferably 100 to 135° C.

GTL (Gas To Liquid derived base oils) synthesized by the Fischer-Tropsch technique of converting natural gas to a liquid fuel is ideal as the base oil according to the present invention, since it has extremely low total sulphur and total aromatics and its paraffin constituent ratio is extremely high, and since it is of excellent oxidation stability and shows very little evaporation loss, compared with mineral base oil refined from crude oil. Though there is no particular restriction regarding the viscous properties of the GTL base oil, usually the viscosity index will be 130 to 180, more preferably 140 to 175. The kinetic viscosity at 40° C. is preferably 2 to 680 mm²/s and even more preferably 5 to 120 mm²/s. Also the total sulphur is usually less than 10 ppm, and the total nitrogen less than 1 ppm. An example of such a GTL base oil product is SHELL XHVI (Registered Trademark).

As group IV oils, there may be mentioned by way of example polyolefins, and as group V oils, there may be mentioned by way of example synthetic oils such as alkyl benzenes, alkyl naphthalenes, esters, polyoxyalkylene glycols, polyphenyl ethers, dialkyl diphenyl ethers, fluorine-containing compounds (for example perfluoro polyethers, or fluorinated polyolefins), or silicone oils.

The polyolefins referred to above include polymers of various types of olefins and hydrides of these. Although the olefins may be chosen at will, specific examples that may be given include ethylene, propylene, butene, or α-olefins of carbon number 5 or more. In the manufacture of the polyolefins, one of the above olefins may be employed alone, or two or more may be employed in combination. In particular, polyolefins called poly-α-olefins (PAO) are ideal.

Although there is no particular restriction regarding the viscosity of these synthetic base oils, their kinetic viscosity at 40° C. is preferably 2 to 680 mm²/s, and even more preferably 8 to 220 mm²/s.

Although there is no particular restriction regarding the content of the above base oil in the lubricating oil composition according to the present invention, the content may be 60 weight % or more, preferably at least 80 weight %, more preferably at least 90 weight % and yet more preferably at least 95 weight % with reference to the total amount of the lubricating oil composition.

A lubricating oil composition may be obtained by including at least one additive selected from acid amides, sarcosinic acid or aspartic acid derivatives in the above base oils. These additives chiefly have a rustproofing effect.

The above acid amides are suitably acid amide compounds obtainable by reacting an amine with a saturated monocarboxylic acid having from 18 to 24 carbons or an unsaturated monocarboxylic acid having from 12 to 30 carbon atoms. Examples that may be mentioned include laurylamide, myristylamide, palmitylamide, stearylamide, isostearylamide, or oleylamide. Also, polyalkylene polyamides obtained by reacting with polyalkylamines, or carboxylic acid amides such as for example isostearyl triethylene tetramide, isostearyl tetraethylene pentamide, isostearyl pentaethylene hexamide, oleyl diethylene triamide, or oleyl diethanolamide may suitably be employed.

The above sarcosinic acid is preferably a glycine derivative showing the following general formula 1:—

(where, in Formula 1, R indicates a straight chain or branched alkyl group or alkenyl group having 1 to 30 carbon atoms).

Specific examples of the above sarcosinic acid that may be given include (Z)-N-methyl-N-(1-oxo-9-octadecenyl) glycine having the following formula 2:—

The preferred aspartic acid derivatives are indicated by the following general formula (3):—

In the above general formula 3, X1 and X2 are respectively hydrogen or alkyl groups, or hydroxyalkyl groups having from 3 to 6 carbons, that may be the same or different, and may preferably respectively be 2-methylpropyl groups or tertiary butyl groups.

X3 may be an alkyl group or alkenyl group, alkyl group having an ether bond, or a hydroxyalkyl group, having 1 to 30 carbons. For example, it may be an octadecyl group, alkoxypropyl group, hydrocarbon oxyalkyl group in which the carbon number of the hydrocarbon is 6 to 18 and the carbon number of the alkyl group is 3 to 6 or, more preferably, a cyclohexyl oxypropyl group, 3-octyl oxypropyl group, 3-iso-octyl oxypropyl group, 3-decyl oxypropyl group, 3-isodecyl oxypropyl group, three-dodecyl oxypropyl group, 3-tetradecyl oxypropyl group, or 3-hexadecyl oxypropyl group.

X4 may be a saturated or unsaturated carboxylic acid group having 1 to 30 carbons, or an alkyl group or alkenyl group having 1 to 30 carbons or a hydroxyalkyl group. Examples are a propionic acid group or propionylic acid group.

The aspartic acid derivative may be of acid value 10 to 200 mgKOH/g, preferably 50 to 150 mgKOH/g, as determined by JIS K2501. The aspartic acid derivative may be employed in the amount of about 0.01 to 5 weight %, preferably about 0.05 to 2 weight %, in the lubricating oil composition.

There is no particular restriction regarding the content of the above acid amide, sarcosinic acid, or aspartic acid derivatives, and this may be 0.01 to 5 weight %, preferably 0.05 to 4.5 weight %, more preferably 0.05 to 4 weight %, even more preferably 0.05 to 3.5 weight % and yet more preferably 0.05 to 3 weight % with respect to the total amount of lubricating oil composition. If the content of these is less than 0.01 weight %, there is a risk that sufficient rustproofing performance will not be achieved, and if the content of these exceeds 5 weight %, there is a risk of a decrease in anti-emulsification performance and foaming performance.

A phosphorus compound may be added to the lubricating oil composition according to the present invention and further improvement in wear-resistance and extreme pressure performance may thereby be conferred. Examples that may be mentioned of suitable phosphorus compounds according to the present invention include: phosphorus-containing carboxylic acids, phosphorus-containing carboxylic acid esters, acid phosphoric acid esters, amine salts of acid phosphoric acid esters, phosphorous acid esters, phosphorothionates, metallic salts of thiophosphoric acid, metallic salts of thiocarbamic acid, and thiocarbamic acid esters. One, or a combination of more than one, of these phosphorus compounds may be employed in a range of 0.01 to 2 weight % with respect to 100 weight % of base oil.

As the phosphorus-containing carboxylic acids or phosphorus-containing carboxylic acid compounds such as esters thereof, so long as these contain both a carboxylic group and a phosphorus atom in the same molecule, there is no particular restriction as to their structure; however, from the point of view of extreme pressure performance and heat/oxidation stability, phosphorylated carboxylic acids or phosphorylated carboxylic acid esters are preferable.

As phosphorylated carboxylic acids and phosphorylated carboxylic acid esters, compounds represented by for example the following formula (4) may be mentioned by way of example.

(where, in the above formula 4, R4 and R5 may be the same or different and respectively indicate a hydrogen atom or hydrocarbon group having 1 to 30 carbons; R6 indicates an alkylene group having 1 to 20 carbons; R7 indicates a hydrogen atom or a hydrocarbon group having 1 to 30 carbons; X1, X2, X3 and X4 may be the same or different, and respectively indicate an oxygen atom or a sulphur atom.

As the hydrocarbon groups having 1 to 30 carbons in R4 and R5 in the above general formula (4), examples that may be given include alkyl groups, alkenyl groups, aryl groups, alkylaryl groups or arylalkyl groups.

Of the above phosphorylated carboxylic acids, useful β-dithio phosphorylated propanoic acids have the structure of the following general formula (5).

A specific example of such β-dithiophosphorylated propanoic acid that may be mentioned is 3-(di-isobutoxy-thiophosphorylsulfanyl)-2-methyl-propanoic acid.

There is no particular restriction regarding the content of phosphorus-containing carboxylic acid compounds in the present lubricating oil composition, but this content is preferably 0.001 to 1 weight %, more preferably 0.002 to 0.5 weight % with respect to the total quantity of the lubricating oil composition.

If the content of phosphorus-containing carboxylic acid compounds is less than the above lower limit, sufficient lubricating performance tends not to be obtained. On the other hand, if more than the above upper limit is added, a lubrication improving effect matching the added content tends not to be attained, and, furthermore, there is a risk of impairment of heat/oxidation stability and/or hydrolysis stability, so this is therefore undesirable.

It should be noted that, in the phosphorylated carboxylic acids represented by the above general formula (4), the content of compounds in which R7 is a hydrogen atom is preferably 0.001 to 0.1 weight %, more preferably 0.002 to 0.08 weight %, even more preferably 0.003 to 0.07 weight %, yet more preferably 0.004 to 0.06 weight %, and still more preferably 0.005 to 0.05 weight %.

Specific examples of the above acid phosphoric acid esters that may be given include: monobutyl acid phosphate, monopentyl acid phosphate, monohexyl acid phosphate, monoheptyl acid phosphate, mono-octyl acid phosphate, monononyl acid phosphate, monodecyl acid phosphate, monoundecyl acid phosphate, monododecyl acid phosphate, monotridecyl acid phosphate, monotetradecyl acid phosphate, monopentadecyl acid phosphate, monohexadecyl acid phosphate, monoheptadecyl acid phosphate, mono-octadecyl acid phosphate, mono-oleyl acid phosphate, dibutyl acid phosphate, dipentyl acid phosphate, dihexyl acid phosphate, diheptyl acid phosphate, dioctyl acid phosphate, dinonyl acid phosphate, didecyl acid phosphate, diundecyl acid phosphate, didodecyl acid phosphate, ditridecyl acid phosphate, ditetradecyl acid phosphate, dipentadecyl acid phosphate, dihexadecyl acid phosphate, diheptadecyl acid phosphate, dioctadecyl acid phosphate or dioleyl acid phosphate.

As the amine salts of acid phosphoric acid esters, there may be mentioned for example salts of the acidic phosphoric acid esters with amines such as methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, heptylamine, octylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, dihexylamine, diheptylamine, dioctylamine, trimethylamine, triethylamine, tripropylamine, tributylamine, tripentylamine, trihexylamine, triheptylamine and trioctylamine.

As the phosphorous acid esters there may be mentioned for example dibutyl phosphite, dipentyl phosphite, dihexyl phosphite, diheptyl phosphite, dioctyl phosphite, dinonyl phosphite, didecyl phosphite, diundecyl phosphite, didodecyl phosphite, dioleyl phosphite, diphenyl phosphite, dicresyl phosphite, tributyl phosphite, tripentyl phosphite, trihexyl phosphite, triheptyl phosphite, trioctyl phosphite, trinonyl phosphite, tridecyl phosphite, triundecyl phosphite, tridodecyl phosphite, trioleyl phosphite, triphenyl phosphite, or tricresyl phosphite.

Specific examples of the phosphorothionates that may be mentioned include tributyl phosphorothionate, tripentyl phosphorothionate, trihexyl phosphorothionate, triheptyl phosphorothionate, trioctyl phosphorothionate, trinonyl phosphorothionate, tridecyl phosphorothionate, triundecyl phosphorothionate, tridodecyl phosphorothionate, tritridecyl phosphorothionate, tritetradecyl phosphorothionate, tripentadecyl phosphorothionate, trihexadecyl phosphorothionate, triheptadecyl phosphorothionate, trioctadecyl phosphorothionate, trioleyl phosphorothionate, triphenyl phosphorothionate, tricresyl phosphorothionate, trixylenyl phosphorothionate, cresyl diphenyl phosphorothionate, xylenyl diphenyl phosphorothionate, tris(n-propylphenyl) phosphorothionate, tris(isopropylphenyl) phosphorothionate, tris(n-butylphenyl) phosphorothionate, tris(isobutylphenyl) phosphorothionate, tris(s-butylphenyl) phosphorothionate, or tris(t-butylphenyl) phosphorothionate. Mixtures of these may also be employed.

The above thiophosphoric acid ester derivatives include esters and metal salts. Specifically, as thiophosphoric acid ester compounds, there may be mentioned by way of example aliphatic thiophosphoric acid esters such as for example tri-isopropyl thiophosphate, tributyl thiophosphate, ethyl dibutyl thiophosphate, trihexyl thiophosphate, tri-2-ethyl hexyl thiophosphate, trilauryl thiophosphate, tristearyl thiophosphate, and trioleyl thiophosphate; and aromatic thiophosphoric acid esters such as for example benzylphenyl thiophosphate, allyl diphenyl thiophosphate, triphenyl thiophosphate, tricresyl thiophosphate, ethyl diphenyl thiophosphate, cresyl diphenyl thiophosphate, dicresyl diphenyl thiophosphate, ethylphenyl diphenyl thiophosphate, diethylphenyl phenyl thiophosphate, propylphenyl diphenyl thiophosphate, dipropylphenyl phenyl thiophosphate, triethyl phenyl thiophosphate, tripropyl phenyl thiophosphate, butylphenyl diphenyl thiophosphate, dibutylphenyl diphenyl thiophosphate, and tributylphenyl thiophosphate.

Specific thiophosphoric acid metal salts include zinc dithiophosphate or molybdenum dithiophosphate: specific examples of zinc dithiophosphates that may be mentioned typically include zinc dialkyl dithiophosphates, zinc diaryl dithiophosphates, or zinc arylalkyl dithiophosphates. For example zinc dialkyl dithiophosphates may be employed wherein the alkyl group of the zinc dialkyl dithiophosphate is a primary or secondary alkyl group of carbon number 3 to 22, or having an alkylaryl group substituted by an alkyl group having 3 to 18 carbons.

Specific examples of the zinc dialkyl dithiophosphates that may be mentioned include zinc dipropyl dithiophosphate, zinc dibutyl dithiophosphate, zinc dipentyl dithiophosphate, zinc dihexyl dithiophosphate, zinc diisopentyl dithiophosphate, zinc diethylhexyl dithiophosphate, zinc dioctyl dithiophosphate, zinc dinonyl dithiophosphate, zinc didecyl dithiophosphate, zinc didodecyl dithiophosphate, zinc dipropylphenyl dithiophosphate, zinc dipentylphenyl dithiophosphate, zinc dipropylmethylphenyl dithiophosphate, zinc dinonyl phenyl dithiophosphate, or zinc didodecylphenyl dithiophosphate.

Specific examples of the molybdenum dithiophosphates that may be mentioned typically include molybdenum dialkyl dithiophosphates, molybdenum diaryl dithiophosphates, or molybdenum arylalkyl dithiophosphates. For example molybdenum dialkyl dithiophosphates may be employed wherein the alkyl group of the molybdenum dialkyl dithiophosphate is a primary or secondary alkyl group having 3 to 22 carbons, or having an alkylaryl group substituted by an alkyl group having 3 to 18 carbons.

Specific examples of the molybdenum dialkyl dithiophosphates that may be mentioned include molybdenum dipropyl dithiophosphate, molybdenum dibutyl dithiophosphate, molybdenum dipentyl dithiophosphate, molybdenum dihexyl dithiophosphate, molybdenum diisopentyl dithiophosphate, molybdenum diethylhexyl dithiophosphate, molybdenum dioctyl dithiophosphate, molybdenum dinonyl dithiophosphate, molybdenum didecyl dithiophosphate, molybdenum didodecyl dithiophosphate, molybdenum dipropylphenyl dithiophosphate, molybdenum dipentylphenyl dithiophosphate, molybdenum dipropylmethylphenyl dithiophosphate, molybdenum dinonyl phenyl dithiophosphate, or molybdenum didodecylphenyl dithiophosphate.

The above thiocarbamic acid ester derivatives include esters and metal salts. Specifically, there may be mentioned by way of example dithiocarbamic acid esters and dithiocarbamic acid metal salts.

As dithiocarbamic acid esters, there may be specifically mentioned by way of example methyldibutyl dithiocarbamate, ethyldipropyl dithiocarbamate, decyldibutyl dithiocarbamate, hexyldidecyl dithiocarbamate, octadecyldiisopropyl dithiocarbamate, octylmethylpropyl dithiocarbamate, and isobutylpropyl-decyl dithiocarbamate.

Of these dithiocarbamic acid metal salts, zinc or molybdenum salts are particularly useful. As specific examples of molybdenum dialkyl dithiocarbamates, there may be mentioned by way of example: molybdenum dibutyl dithiocarbamate sulphide, molybdenum dipentyl dithiocarbamate sulphide, molybdenum dihexyl dithiocarbamate sulphide, molybdenum diheptyl dithiocarbamate sulphide, molybdenum dioctyl dithiocarbamate sulphide, molybdenum dinonyl dithiocarbamate sulphide, molybdenum didecyl dithiocarbamate sulphide, molybdenum diundecyl dithiocarbamate sulphide, molybdenum didodecyl dithiocarbamate sulphide, molybdenum ditridecyl dithiocarbamate sulphide, oxy-molybdenum dibutyl dithiocarbamate sulphide, oxy-molybdenum dipentyl dithiocarbamate sulphide, oxy-molybdenum dihexyl dithiocarbamate sulphide, oxy-molybdenum diheptyl dithiocarbamate sulphide, oxy-molybdenum dioctyl dithiocarbamate sulphide, oxy-molybdenum dinonyl dithiocarbamate sulphide, oxy-molybdenum didecyl dithiocarbamate sulphide, oxy-molybdenum diundecyl dithiocarbamate sulphide, oxy-molybdenum didodecyl dithiocarbamate sulphide, and oxy-molybdenum ditridecyl dithiocarbamate sulphide.

In order to further improve performance, various additives may be suitably employed as required. Examples of these additives that may be mentioned include antioxidants, metal deactivators, extreme pressure agents, oiliness improvers, anti-foaming agents, viscosity index improvers, pour-point depressants, detergent-dispersants, rust inhibitors, demulsifiers etc. or other known lubricating oil additives.

As the antioxidants that may be employed in the present invention, antioxidants that are employed in lubricating oils are practically preferable; examples that may be mentioned include: amine-based antioxidants, phenol-based antioxidants, sulphur-based antioxidants and phosphorus-based antioxidants. One or a combination of more than one of these antioxidants may be employed in the range of 0.01 to 5 weight % with respect to 100 weight % of base oil.

Examples of the amine-based antioxidants that may be given include: dialkyl diphenylamines such as p,p′-dioctyl diphenylamine (manufactured by Seiko Chemicals Inc: Non-flex OD-3), p,p′-di-α-methylbenzyl diphenylamine, or N-p-butylphenyl-N-p′-octyl phenylamine; monoalkyl diphenylamines such as mono-t-butyl diphenylamine or mono-octyl diphenylamine; bis(dialkyl phenyl)amines such as di(2,4-diethyl phenyl)amine, or di(2-ethyl-4-nonylphenyl)amine; alkyl phenyl-1-naphthylamines such as octyl phenyl-1-naphthylamine or N-t-dodecyl phenyl-1-naphthylamine; aryl-naphthylamines such as 1-naphthylamine, phenyl-1-naphthylamine, phenyl-2-naphthylamine, N-hexyl phenyl-2-naphthylamine, or N-octyl phenyl-2-naphthylamine; phenylene diamines such as N,N′-diisopropyl-p-phenylene diamine, or N,N′-diphenyl-p-phenylenediamine; or phenothiazines such as phenothiazine (manufactured by Hodogaya Chemicals Inc: Phenothiazine) or 3,7-dioctyl phenothiazine.

As the sulphur-based antioxidants, there may be mentioned by way of example dialkyl sulphides such as didodecyl sulphide or dioctadecyl sulphide, thiodipropionic acid esters such as didodecyl thiodipropionate, dioctadecyl thiodipropionate, dimyristyl thiodipropionate, or dodecyl octadecyl thiodipropionate, or 2-mercaptobenzoimidazole.

Examples of phenol-based antioxidants include 2-t-butyl phenol, 2-t-butyl-4-methyl phenol, 2-t-butyl-5-methyl phenol, 2,4-di-t-butyl phenol, 2,4-dimethyl-6-t-butyl phenol, 2-t-butyl-4-methoxy phenol, 3-t-butyl-4-methoxy phenol, 2,5-di-t-butyl hydroquinone (manufactured by Kawaguchi Chemicals Inc: Antage DBH), 2,6-di-t-butyl phenol, 2,6-di-t-butyl-4-alkyl phenols, such as 2,6-di-t-butyl-4-methyl phenol, or 2,6-di-t-butyl-4-ethyl phenol; or 2,6-di-t-butyl-4-alkoxy phenols such as 2,6-di-t-butyl-4-methoxy phenol or 2,6-di-t-butyl-4-ethoxy phenol.

Further examples include alkyl-3-(3,5-di-t-butyl-4-hydroxy phenyl) propionates such as 3,5-di-t-butyl-4-hydroxybenzyl mercapto-octyl acetate, n-octadecyl-3-(3,5-di-t-butyl-4-hydroxy phenyl) propionate (manufactured by Yoshitomi Seiyaku Inc: Yoshinox SS), n-dodecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate, 2′-ethylhexyl-3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate, or benzene propanoate 3,5-bis(1,1-dimethyl-ethyl)-4-hydroxy-C₇ to C₉ side-chain alkyl ester (manufactured by Ciba Speciality Chemicals Inc: Irganox L135), or 2,2′-methylene bis(4-alkyl-6-t-butylphenol) such as 2,6-di-t-butyl-α-dimethylamino-p-cresol, 2,2′-methylene bis(4-methyl-6-t-butylphenol) (manufactured by Kawaguchi Chemicals Inc: Antage W-400), or 2,2′-methylene bis(4-ethyl-6-t-butylphenol) (manufactured by Kawaguchi chemicals: Antage W-500).

Yet further examples include bisphenols such as 4,4′-butylidene bis(3-methyl-6-t-butylphenol) (manufactured by Kawaguchi Chemicals Inc: Antage W-300), 4,4′-methylene bis(2,6-di-t-butylphenol) (manufactured by Shell Japan Inc: Ionox 220 AH), 4,4′-bis(2,6-di-t-butylphenol), 2,2-(di-p-hydroxyphenyl) propane (manufactured by Shell Japan Inc: bisphenol A), 2,2-bis(3,5-di-t-butyl-4-hydroxyphenyl)propane, 4,4′-cyclohexylidene bis(2,6-t-butylphenol), hexamethylene glycol bis[3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate] (manufactured by Ciba Speciality Chemicals Inc: Irganox L109), triethylene glycol bis[3-(3-t-butyl-4-hydroxy-5-methyl phenyl)propionate] (manufactured by Yoshitomi Chemicals Inc: Tominox 917), 2,2′-thio-[diethyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] (manufactured by Ciba Speciality Chemicals Inc: Irganox L 115), 3,9-bis{1,1-dimethyl-2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]ethyl} 2,4,8,10-tetraoxaspiro[5,5]undecane (Sumitomo Chemicals: Sumilizer GA80), or 4,4′-thiobis(3-methyl-6-t-butylphenol) (manufactured by Kawaguchi Chemicals Inc: Antage RC), or 2,2′-thiobis(4,6-di-t-butyl-resorcin).

Further examples that may be given also include polyphenols, such as tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate] methane (manufactured by Ciba Speciality Chemicals Inc: Irganox L 101), 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane (manufactured by Yoshitomi Chemicals Inc: Yoshinox 930), 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene (manufactured by Shell Japan Inc: Ionox 330), bis-[3,3′-bis-(4′-hydroxy-3′-t-butylphenyl)butyric acid] glycol ester, 2-(3′,5′-di-t-butyl-4-hydroxyphenyl)methyl-4-(2″,4″-di-t-butyl-3″-hydroxyphenyl)methyl-6-t-butylphenol, or 2,6-bis(2′-hydroxy-3′-t-butyl-5′-methyl-benzyl)-4-methylphenol, or phenol/aldehyde condensation products such as the condensation product of p-t-butylphenol and formaldehyde or the condensation product of p-t-butylphenone and acetaldehyde.

As the phosphorus-based antioxidants, there may be mentioned by way of example triaryl phosphites such as triphenyl phosphite, or tricresyl phosphite, trialkyl phosphites such as trioctadecyl phosphite, or tridecyl phosphite, or tridodecyl trithiophosphite.

Metal deactivators that may be used together with the composition according to the present invention include benzotriazole, 4-alkyl-benzotriazoles such as 4-methyl-benzotriazole, or 4-ethyl-benzotriazole, 5-alkyl-benzotriazoles such as 5-methyl-benzotriazole, or 5-ethyl-benzotriazole, 1-alkyl-benzotriazoles such as 1-dioctyl-aminomethyl-2,3-benzotriazole, benzotriazole derivatives such as 1-alkyl-tolutriazoles such as 1-dioctyl aminomethyl-2,3-tolutriazole, benzoimidazole, 2-(alkyl dithio)-benzoimidazoles such as 2-(octyl dithio)-benzoimidazole, 2-(decyl dithio)-benzoimidazole, or 2-(dodecyl dithio)-benzoimidazole, or benzoimidazole derivatives such as 2-(alkyldithio)-toluimidazoles such as 2-(octyl dithio)-toluimidazole, 2-(decyl dithio)-toluimidazole, or 2-(dodecyl dithio)-toluimidazole.

Further examples include indazole or indazole derivatives such as toluindazoles such as 4-alkyl-indazoles or 5-alkyl-indazoles, benzothiazole, or benzothiazole derivatives such as 2-mercapto benzothiazole derivatives-(Chiyoda Chemicals Inc: Thiolite B-3100), 2-(alkyl dithio) benzothiazoles such as 2-(hexyl dithio) benzothiazole or 2-(octyl dithio) benzothiazole, 2-(alkyl dithio) toluthiazoles such as 2-(hexyl dithio) toluthiazole or 2-(octyl dithio) toluthiazole, 2-(N,N-dialkyl dithiocarbamyl)benzothiazoles such as 2-(N,N-diethyl dithiocarbamyl)benzothiazole, 2-(N,N-dibutyl dithiocarbamyl)benzothiazole or 2-(N,N-dihexyl dithiocarbamyl)benzothiazole, or 2-(N,N-dialkyl dithiocarbamyl) toluthiazoles such as 2-(N,N-diethyl dithiocarbamyl) toluthiazole, 2-(N,N-dibutyl dithiocarbamyl) toluthiazole or 2-(N,N-dihexyl dithiocarbamyl) toluthiazole.

Yet further examples include benzo-oxazole derivatives such as 2-(alkyl dithio)-benzo-oxazoles such as 2-(octyl dithio) benzo-oxazole, 2-(decyl dithio) benzo-oxazole, or 2-(dodecyl dithio) benzo-oxazole, or 2-(alkyl dithio)-toluoxazoles such as 2-(octyl dithio) toluoxazole, 2-(decyl dithio) toluoxazole, or 2-(dodecyl dithio) toluoxazole, thiadiazole derivatives such as 2,5-bis(alkyl dithio)-1,3,4-thiadiazoles such as 2,5-bis(heptyl dithio)-1,3,4-thiadiazole, 2,5-bis(nonyl dithio)-1,3,4-thiadiazole, 2,5-bis(dodecyl dithio)-1,3,4-thiadiazole or 2,5-bis(octadecyl dithio)-1,3,4-thiadiazole, such as 2,5-bis(N,N-dialkyl dithiocarbamyl)-1,3,4-thiadiazoles such as 2,5-bis(N,N-diethyl dithiocarbamyl)-1,3,4-thiadiazole, 2,5-bis(N,N-dibutyl dithiocarbamyl)-1,3,4-thiadiazole, or 2,5-bis(N,N-dioctyl dithiocarbamyl)-1,3,4-thiadiazole, or 2-N,N-dialkyl dithiocarbamyl-5-mercapto-1,3,4-thiadiazoles such as 2-N,N-dibutyl dithiocarbamyl-5-mercapto-1,3,4-thiadiazole or 2-N,N-dioctyl dithiocarbamyl-5-mercapto-1,3,4-thiadiazole, or triazole derivatives such as 1-alkyl-2,4-triazoles such as 1-di-octyl aminomethyl-2,4-triazole.

One, or a combination of more than one, of these metal deactivators may be employed in a range of 0.01 to 0.5 weight % with respect to 100 weight % of base oil.

Polyhydric alcohol fatty acid esters may be blended with the lubricating oil composition according to the present invention with the object of improving oiliness. For example partial or complete esters of saturated or unsaturated fatty acids having 1 to 24 carbons of polyhydric alcohols such as glycerol, sorbitol, alkylene glycols, neopentyl glycol, trimethylol propane, pentaerythritol or xylitol may be employed.

As glycerol esters, there may be mentioned by way of example glycerol monolaurate, glycerol monostearate, glycerol monopalmitate, glycerol mono-oleate, glycerol dilaurate, glycerol distearate, glycerol dipalmitate or glycerol dioleate.

As sorbitol esters, there may be mentioned by way of example sorbitol monolaurate, sorbitol monopalmitate, sorbitol monostearate, sorbitol mono-oleate, sorbitol dilaurate, sorbitol dipalmitate, sorbitol distearate, sorbitol dioleate, sorbitol tristearate, sorbitol trilaurate, sorbitol trioleate, or sorbitol tetraoleate.

As alkylene glycol esters, there may be mentioned by way of example ethylene glycol monolaurate, ethylene glycol monostearate, ethylene glycol mono-oleate, ethylene glycol dilaurate, ethylene glycol distearate, ethylene glycol dioleate, propylene glycol monolaurate, propylene glycol monostearate, propylene glycol mono-oleate, propylene glycol dilaurate, propylene glycol distearate or propylene glycol dioleate.

As neopentyl glycol esters, there may be mentioned by way of example neopentyl glycol monolaurate, neopentyl glycol monostearate, neopentyl glycol mono-oleate, neopentyl glycol dilaurate, neopentyl glycol distearate, or neopentyl glycol dioleate.

As trimethylol propane esters, there may be mentioned by way of example trimethylol propane monolaurate, trimethylol propane monostearate, trimethylol propane mono-oleate, trimethylol propane dilaurate, trimethylol propane distearate, trimethylol propane dioleate, or pentaerythritol monolaurate.

As pentaerythritol esters, there may be mentioned by way of example pentaerythritol monostearate, pentaerythritol mono-oleate, pentaerythritol dilaurate, pentaerythritol distearate, pentaerythritol dioleate, or pentaerythritol mono-oleate.

As fatty acid esters of such polyhydric alcohols, preferably partial esters of polyhydric alcohols and unsaturated fatty acids are employed.

In order to improve low temperature fluidity or viscosity performance in respect of the lubricating oil composition according to the present invention, pour-point depressants or viscosity index improving agents may be added.

As viscosity index improving agents, there may be mentioned by way of example non-dispersive viscosity index improving agents such as polymethacrylate or ethylene-propylene copolymer, styrene-diene copolymer, or olefin polymers such as poly-isobutylene, or polystyrene, or dispersive viscosity index improving agents obtained by copolymerization of a nitrogen-containing monomer with these. These may be employed in a range of 0.05 to 20 weight % with respect to 100 weight % of base oil.

As pour-point depressants, there may be mentioned by way of example polymethacrylate-based polymers. These may be employed in a range of 0.01 to 5 weight % with respect to 100 weight % of base oil.

In order to confer anti-foaming properties on the lubricating oil composition according to the present invention, an anti-foaming agent may be added. As anti-foaming agents suitable in the present invention, known anti-foaming agents that are generally employed as ordinary lubricating oil additives may be used. There may be mentioned by way of example organosilicates such as dimethyl polysiloxane, diethyl silicate, or fluorosilicones, or non-silicone anti-foaming agents such as polyalkylacrylates. These may be employed either alone or in a combination of two or more thereof, in a range of 0.0001 to 0.1 weight % with respect to 100 weight % of base oil.

As anti-emulsifiers suitable in the present invention, there may be mentioned by way of example known anti-emulsifiers that are employed as ordinary lubricating oil additives. These may be employed in a range of 0.005 to 0.5 weight % with respect to 100 weight % of base oil.

EXAMPLES

The present invention is further specifically described below with reference to Examples and Comparative Examples: however, the present invention is not restricted in any way to the following Examples.

In preparation of Examples 1 to 17 and Comparative Examples 1 to 4, base oils and additives of the following compositions were prepared.

(1) Base oil A: PAO (poly-α-olefins) (properties: —kinetic viscosity at 100° C.: 6.36 mm²/s; viscosity index: 136; total sulphur (value calculated as elementary sulphur): less than 5 weight ppm) (2) Base oil B: group 1 paraffin-based mineral oil: mineral oil obtained by blending HVI60 (registered trademark) and HVI160S (registered trademark), which are paraffin-based mineral oils obtained by employing in suitable combination purifying means such as solvent dewaxing on the lubricating oil fraction obtained by reduced pressure distillation of crude oil, to adjust the viscosity to ISO VG #32 (properties: —kinetic viscosity at 100° C.: 5.45 mm²/s; viscosity index: 104; total sulphur (value calculated as elementary sulphur): 0.5 weight %=5000 weight ppm) (3) Base oil C: base oil obtained by blending GTL (gas to liquid) base oil synthesised using the Fischer-Tropsch method technology for converting natural gas to liquid fuel to adjust the viscosity to ISO VG No. 32 (properties: —kinetic viscosity at 100° C.: 6.25 mm²/s; viscosity index: 145; total sulphur (value calculated as elementary sulphur): less than 10 weight ppm). (4) Additive A1: polyalkylene polyamide (manufactured by Chevron Inc: Oloa340D) (5) Additive A2: oleyl sarcosinic acid (manufactured by Ciba Speciality Chemicals Inc: Sarcosyl O) (6) Additive A3: aspartic acid derivative (manufactured by King Inc: K-corr100) (7) Additive A4: synthetic Ca sulfonate (manufactured by in Infineum Inc: Infineum 9330) (8) Additive A5: alkenyl succinic acid ester (manufactured by Lubrizol Inc: Lubrizol 859) The above additives A1 to A5 act chiefly as rustproofing agents. (9) Additive B1: β-dithiophosphorylated propionic acid (manufactured by Ciba Speciality Chemicals Irgalube 353) (10) Additive B2: octyl acid phosphate (11) Additive B3: zinc dialkyl dithiophosphate (ZnDTP manufactured by Lubrizol: Lubrizol 1095) (12) Additive B4: zinc dialkyl dithiophosphate (ZnDTP manufactured by Lubrizol: Lubrizol 1375) (13) Additive B5: molybdenum dialkyl dithiophosphate (MoDTP manufactured by Vanderbilt Inc: MolyvanL) (14) Additive B6: molybdenum dialkyl dithiocarbamate (MODTC manufactured by Adeka Inc: Sakuralube 165) (15) Additive B7: molybdenum dialkyl dithiocarbamate (MODTC manufactured by Kechen OX77M) The above additives B1 to B7 act chiefly as wear adjustment agents. (16) Additive C1: alkylated diphenylamine (manufactured by Ciba Speciality Chemicals: IrganoxL57) (17) Additive C2: phenol antioxidants (manufactured by Ciba Speciality Chemicals: IrganoxL135)

The above additives C1 to C2 act chiefly as antioxidants.

Lubricating oils according to Examples 1 to 17 having the compositions shown in Table 1 to Table 4 and Comparative Examples 1 to 4 shown in Table 5 were prepared using the above base oils and additives. Also, commercially available machine tool lubricating oil was prepared as Comparative Example 5. The amounts of the various components of the compositions of Tables 1 to 5 are expressed in terms of weight %.

Measurement of Properties

In order to ascertain the properties of the various lubricating oil compositions of the above Examples 1 to 17 and Comparative Examples 1 to 5, the kinetic viscosity at 40° C. (in accordance with JIS K2283), the kinetic viscosity at 100° C. (in accordance with JS K2283), the viscosity index (in accordance with JIS K2283) and the oxygen value (in accordance with JIS K2501) were measured.

The various measurement results are shown in Table 1 to Table 5.

Tests

Using the various lubricating oil compositions of Examples 1 to 17 and Comparative Examples 1 to 5, the following tests were conducted in order to ascertain the properties.

Rustproofing Test

In accordance with JIS K2510, 300 ml of sample oil were taken in a container arranged in a constant temperature bath, stirring conducted by rotating at 1000 rpm, and an iron test piece was inserted in the sample oil when a temperature of 60° C. had been reached: 30 ml of artificial seawater was then added, and stirring continued for 24 hours, maintaining the temperature at 60° C. The test piece was then extracted, and a visual evaluation as to whether or not rusting of the test piece had occurred was conducted.

-   -   The evaluation criteria were as follows:—     -   No rust: no generation of rust was seen (0%)     -   Slight: no more than six rust spots, of no more than 1 mm;

Moderate: more than Slight as described above, but less than 5% of the surface area; and

High: more than Moderate as described above: at least 5% of the surface area.

Ceramics Lubrication Performance Test

The lubricating properties of the various lubricating oil compositions were evaluated by performing a Shell 4-ball abrasion test, using the test method standardised in ASTMD 4172. The conventional Shell 4-ball abrasion test is conducted under the test conditions of comparatively low rotational speed (slippage rate) of 1200 m⁻¹, to 1800 m⁻¹, but, in view of the actual conditions of use, the following more severe test was conducted, and the measured rate of rise of oil temperature, maximum torque, frictional coefficient and value of the diameter of wear-marks of the fixed ball were converted to an index of lubrication performance evaluation.

Test Conditions

Test balls: for the rotating balls, ceramics (Si₃N₄), and for the fixed ball, bearing steel (SUJ-24) were employed.

Load (P): 40.0 kgf (=392 N)

Rotational speed: 6000 m⁻¹

Test time: 30 minutes

Temperature: room temperature (at start of test)

Measurement: during the period from the start of the test to its end, the frictional torque (coefficient of friction) and test oil temperature and room temperature were automatically measured, and the rate of rise of oil temperature (° C./10 s), maximum torque (kgf·cm), and coefficient of friction were found by the following expression. Also, the diameter of the wear marks of the SUJ-2 ball (fixed ball) after completion of the test was measured.

Coefficient of friction=T/(0.4488×p)

[where T is the frictional torque (kgf·cm) and P is the load (kgf)]

1 kgf=9.80665 m, 1 kgf·cm=9.80665 N·cm.

Grading of Measurement Results

(1) Wear Mark Diameter

-   -   @: less than 0.7     -   ◯: at least 0.7 but less than 1.0     -   X: at least 1.0

(2) Rate of Rise of Temperature

-   -   @: less than 0.15     -   ◯: at least 0.15 but less than 0.2     -   X: at least 0.2

(3) Maximum Torque

-   -   @: less than 1.8     -   ◯: at least 1.8 but less than 2.7     -   X: at least 2.7

(4) Coefficient of Friction

-   -   @: less than 0.100     -   ◯: at least 0.100 but less than 0.150     -   X: at least 0.150

Test Results

The results of the various tests are shown in Table 1 to Table 5.

Evaluation

In the case where the polyalkylene polyamide of Additive A1 was blended with the base oil A (PAO) of Example 1, no generation of rust was observed and excellent results were obtained in the Shell 4-ball wear test. Also, in the case of Example 2, in which the additives C1, C2 were added as antioxidants to Example 1, the wear marks were small. Also in the case of Example 3, in which the oleyl sarcosinic acid of additive A2 was employed instead of the additive A1 of Example 2, and in the case of Example 4, in which the aspartic acid derivative of additive A3 was employed, no generation of rust was observed, and excellent results were obtained with the Shell 4-ball wear test.

In the case of Examples 5, 6, 7, in which the additive B1 i.e. β-dithiophosphorylated propionic acid was added to the above Examples 2, 3, 4, no generation of rust was observed, excellent results were obtained in the Shell 4-ball wear test, and the diameter of wear marks was small.

In the case of Examples 8 and 9, in which the base oil A of Example 5 was altered to the paraffin-based mineral oil of group 1 of base oil B, or the GTL base oil of base oil C, excellent results were obtained substantially similar to those of Example 5.

In the case of Example 10, the octyl acid phosphate of additive B2 was employed instead of the additive B1 of Example 5: this Example can also be used as a lubricating oil composition.

In the case of Examples 11 and 12, instead of the additive A1 of Example 10, additives A1+A2 or additives A1+A3 were both employed together: even better results than in the case of Example 10 were obtained.

In the case of Examples 13 to 17, in place of the octyl acid phosphate of additive B2 in Example 10, there were successively employed the zinc dialkyldithiophosphate of additive B3, the zinc dialkyldithiophosphate of additive B4, the molybdenum dialkyldithiophosphate of additive B5, the molybdenum dialkyldithiocarbamate of additive B6, or the molybdenum dialkyl dithiocarbamate of additive B7: these also can be suitably employed as lubricating oil compositions.

In the above Examples, Examples 5 to 12 indicate compositions that are ideal in particular as lubricating oil compositions for ceramics ball antifriction bearings.

In contrast, in the case of base oil A of comparative example 1, in the rustproofing test a high degree of rust was generated, and poor results were obtained in that the rate of temperature rise of the oil, the maximum torque and coefficient of friction in the Shell 4-ball wear test were large, and the diameter of the wear marks was large. In the case where the alkylated diphenylamine of additive C1 and the phenol-based antioxidant of additive C2 were added to the base oil A of Comparative Example 2, although good results were obtained in the Shell 4-ball wear test, a high degree of rust was generated in the rustproofing test. In the case where the synthetic Ca sulfonate of additive A4 and the above additives C1+C2 of Comparative Example 3 were employed, no rust was generated in the rustproofing test, but the results in the Shell 4-ball wear test were poor. Also, although this Shell 4-ball wear test should nominally be performed for 1800 seconds, after 430 seconds, smoke was generated, giving rise to risk of catching fire, so the test was interrupted. In the case where the alkenyl succinic acid ester of additive A5 and the above additives C1+C2 of Comparative Example 4 were employed, no rust was generated in the rustproofing test, but the results in the Shell 4-ball wear test were poor. Also, in the case of the commercial lubricating oil for machine tools of Comparative Example 5, generation of rust was not observed, but the results in the Shell 4-ball wear test were poor.

Thus, in the Comparative Examples, in all cases it was found that the standard required for use as a ceramics ball antifriction bearing lubricating oil was not satisfied, with the result that these Comparative Examples were not suitable for use as a high speed main shaft oil/air lubricating oil employing ceramics ball antifriction bearings.

TABLE 1 Example 1 Example 2 Example 3 Example 4 Base oil A 99.95 99.70 99.72 99.70 Additive A1 0.05 0.05 Additive A2 0.03 Additive A3 0.05 Additive C1 0.05 0.05 0.05 Additive C2 0.20 0.20 0.20 Viscosity mm²/s @40° C. JIS K 2283 34.8 34.8 34.8 34.8 Viscosity mm²/s @100° C. JIS K 2283 6.36 6.35 6.35 6.36 Viscosity index JIS K 2283 135 135 135 135 Acid value mgKOH/g JIS K 2501 0.00 0.01 0.05 0.06 Rustproofing performance JIS K 2510 No rust No rust No rust No rust @60° C. (artificial seawater) Shell 4-ball wear test - based on ASTM D4172 Wear mark diameter (mm) 0.99 0.92 0.79 0.89 Grading ◯ ◯ ◯ ◯ Rate of rise of oil temperature (° C./10 s) 0.12 0.12 0.14 0.13 Grading @ @ @ @ Maximum torque (kgf · cm) 1.4 1.5 1.8 1.4 Grading @ @ ◯ @ Coefficient of friction 0.078 0.084 0.100 0.078 Grading @ @ ◯ @ Test time (sec) 1,800 1,800 1,800 1,800

TABLE 2 Example 5 Example 6 Example 7 Example 8 Example 9 Base oil A 99.67 99.69 99.67 Base oil B 99.67 Base oil C 99.67 Additive A1 0.05 0.05 0.05 Additive A2 0.03 Additive A3 0.05 Additive B1 0.03 0.03 0.03 0.03 0.03 Additive C1 0.05 0.05 0.05 0.05 0.05 Additive C2 0.20 0.20 0.20 0.20 0.20 Viscosity mm²/s JIS K 2283 34.4 34.8 34.8 32.0 32.1 @40° C. Viscosity mm²/s JIS K 2283 6.35 6.35 6.35 5.45 6.27 @100° C. Viscosity index JIS K 2283 137 135 135 105 149 Acid value mgKOH/g JIS K 2501 0.07 0.13 0.11 0.05 0.08 Rustproofing JIS K 2510 No rust No rust No rust No rust No rust performance @60° C. (artificial seawater) Shell 4-ball wear test - based on ASTM D4172 Wear mark diameter (mm) 0.54 0.77 0.88 0.64 0.52 Grading @ ◯ ◯ @ @ Rate of rise of oil (° C./10 s) 0.13 0.15 0.13 0.11 0.12 temperature Grading @ ◯ @ @ @ Maximum torque (kgf · cm) 1.5 1.9 1.5 2.3 1.5 Grading @ ◯ @ ◯ @ Coefficient of friction 0.084 0.106 0.084 0.126 0.084 Grading @ ◯ @ ◯ @ Test time (sec) 1,800 1,800 1,800 1,800 1,800

TABLE 3 Example Example Example 10 11 12 Base oil A 99.35 99.35 99.35 Additive A1 0.05 0.04 0.04 Additive A2 0.01 Additive A3 0.01 Additive B2 0.35 0.35 0.35 Additive C1 0.05 0.05 0.05 Additive C2 0.20 0.20 0.20 Viscosity mm²/ JIS K 2283 34.8 34.9 34.8 s @40° C. Viscosity mm²/ JIS K 2283 6.38 6.36 6.35 s @100° C. Viscosity index JIS K 2283 136 135 135 Acid value mgKOH/g JIS K 2501 1.30 1.39 1.28 Rustproofing JIS K 2510 No rust No rust No rust performance @60° C. (artificial seawater) Wear mark diameter (mm) 0.72 0.69 0.68 Grading ◯ @ @ Rate of rise of oil (° C./10 s) 0.15 0.12 0.08 temperature Grading ◯ @ @ Maximum torque (kgf · cm) 1.9 1.4 1.4 Grading ◯ @ @ Coefficient of friction 0.108 0.079 0.077 Grading ◯ @ @ Test time (sec) 1,800 1,800 1,800

TABLE 4 Example Example 13 Example 14 Example 15 Example 16 17 Base oil A 99.39 99.27 99.24 98.90 99.34 Additive A1 0.05 0.05 0.05 0.05 0.05 Additive B3 0.31 Additive B4 0.43 Additive B5 0.46 Additive B6 0.80 Additive B7 0.36 Additive C1 0.05 0.05 0.05 0.05 0.05 Additive C2 0.20 0.20 0.20 0.20 0.20 Viscosity mm²/s @40° C. JIS K 34.8 34.9 34.9 34.6 34.9 2283 Viscosity mm²/s @100° C. JIS K 6.35 6.36 6.36 6.33 6.36 2283 Viscosity index JIS K 135 135 135 135 135 2283 Acid value mgKOH/g JIS K 0.57 0.47 0.61 0.25 0.35 2501 Rustproofing performance JIS K No rust No rust No rust No rust No rust @60° C. (artificial seawater) 2510 Shell 4-ball wear test - based on ASTM D4172 Wear mark diameter (mm) 0.82 0.93 0.85 0.82 0.90 Grading ◯ ◯ ◯ ◯ ◯ Rate of rise of oil temperature (° C./10 s) 0.17 0.18 0.15 0.11 0.15 Grading ◯ ◯ ◯ @ ◯ Maximum torque (kgf · cm) 1.5 1.9 1.5 2.3 1.5 Grading ◯ ◯ ◯ ◯ @ Coefficient of friction 0.106 0.106 0.145 0.100 0.095 Grading ◯ ◯ ◯ ◯ @ Test time (sec) 1,800 1,800 1,800 1,800 1,800

TABLE 5 Comparative Comparative Comparative Comparative Comparative example 1 example 2 example 3 example 4 example 5 Base oil A 100 99.75 99.70 99.70 Commercial Additive A4 0.05 lubricating oil Additive A5 0.05 Additive B4 0.05 0.05 0.05 Additive C1 0.20 0.20 0.20 Additive C2 34.7 34.7 34.8 34.8 29.1 Viscosity JIS K 6.36 6.34 6.36 6.36 5.19 mm²/s @40° C. 2283 Viscosity JIS K 136 135 135 135 109 mm²/s @100° C. 2283 Viscosity index JIS K 0.00 0.01 0.04 0.09 0.09 2283 Acid value JIS K 100 99.75 99.70 99.70 mgKOH/g 2501 Rustproofing JIS K High-level High-level No rust No rust No rust performance 2510 @60° C. (artificial seawater) Shell 4-ball wear test - based on ASTM D4172 Wear mark (mm) 2.40 1.07 3.06 2.48 2.84 diameter Grading x x x x x Rate of rise of (° C./10 s) 0.64 0.12 0.57 0.55 0.54 oil temperature Grading x @ x x x Maximum (kgf · cm) 7.1 2.1 7.0 7.2 7.3 torque Grading x ∘ x x x Coefficient of 0.395 0.117 0.390 0.401 0.407 friction Grading x ∘ x x x Test time (sec) 1,800 1,800 430 1,800 1,800 

1-12. (canceled)
 13. A lubricating oil composition comprising (a) a base oil and (b) one or more additives selected from the group consisting of: (i) an acid amide obtained by reacting an amine with a saturated monocarboxylic acid having from 12 to 30 carbons or an unsaturated monocarboxylic acid having from 18 to 24 carbons; (ii) sarcosinic acid; and (iii) an aspartic acid derivative.
 14. The lubricating oil composition of claim 13, wherein the amine of the acid amide is a polyalkylamine.
 15. The lubricating oil composition of claim 14, wherein the acid amide is selected from the group consisting of isostearyl triethylene tetramide, isostearyl tetraethylene pentamide, isostearyl pentaethylene hexamide, oleyl diethylene triamide, and oleyl diethanolamide.
 16. The lubricating oil composition of claim 13, wherein the base oil is a synthetic oil.
 17. The lubricating oil composition of claim 16, wherein the synthetic oil is a poly-α-olefin or a GTL derived base oil.
 18. The lubricating oil composition of claim 13, wherein the base oil is a concentration that is at least 60 weight % of the lubricating oil composition and said one or more additives are at combined concentration that is in a range of 0.01 to 5 weight % of the lubricating oil composition.
 19. The lubricating oil composition of claim 13 further comprising (c) one or more phosphorous compounds selected from the group consisting of a phosphorus-containing carboxylic acid, a phosphorus-containing carboxylic acid ester, an acidic phosphoric acid ester, an amine salt of an acidic phosphoric acid ester, a phosphorous acid ester, a phosphorothionate, a thiophosphoric acid ester, a thiophosphoric acid metal salt, a thiocarbamic acid ester, and a thiocarbamic acid metal salt.
 20. The lubricating oil composition of claim 19, wherein the phosphorus-containing carboxylic acid is a β-phosphorylated propionic acid, the phosphorus-containing carboxylic acid ester is a β-dithiophosphorylated propionic acid ester, the thiophosphoric acid metal salt is a zinc dialkyldithiophosphate or a molybdenum dialkyldithiophosphate, and the thiocarbamic acid metal salt is a zinc dithiocarbamate or a molybdenum dithiocarbamate.
 21. The lubricating oil composition of claim 20, wherein the one or more phosphorous compounds are at a combined concentration that is in a range of 0.01 to 2 weight % of the base oil.
 22. The lubricating oil composition of claim 13 further comprising one or more of the following: (d) one or more antioxidants at a combined concentration that is a range of 0.01 to 5 weight % of the base oil; (e) one or more metal deactivators at a combined concentration that is in a range of 0.01 to 0.5 weight % of the base oil; (f) one or more polyhydric alcohol fatty acid esters; (g) one or more pour-point depressants at a combined concentration that is in a range of 0.01 to 5 weight % of the base oil; (h) one or more viscosity index improving agents at a combined concentration that is in a range of 0.05 to 20 weight % of the base oil; (i) one or more anti-foaming agents at a combined concentration that is in a range of 0.0001 to 0.1 weight % of the base oil; and (j) one or more anti-emulsifiers at a combined concentration that is in the range of 0.005 to 0.5 weight % of the base oil.
 23. A method of lubricating an apparatus, the method comprising lubricating the apparatus with a lubricating oil composition that comprises (a) a base oil and (b) one or more additives selected from the group consisting of: (i) an acid amide obtained by reacting an amine with a saturated monocarboxylic acid having from 12 to 30 carbons or an unsaturated monocarboxylic acid having from 18 to 24 carbons; (ii) sarcosinic acid; and (iii) an aspartic acid derivative.
 24. The method of claim 23, wherein the amine of the acid amide is a polyalkylamine.
 25. The method of claim 24, wherein the acid amide is selected from the group consisting of isostearyl triethylene tetramide, isostearyl tetraethylene pentamide, isostearyl pentaethylene hexamide, oleyl diethylene triamide, and oleyl diethanolamide.
 26. The method of claim 23, wherein the base oil is a synthetic oil.
 27. The method of claim 26, wherein the synthetic oil is a poly-α-olefin or a GTL derived base oil.
 28. The method of claim 23, wherein the base oil is a concentration that is at least 60 weight % of the lubricating oil composition and said one or more additives are at combined concentration that is in a range of 0.01 to 5 weight % of the lubricating oil composition.
 29. The method of claim 23, wherein the lubricating oil composition further comprises (c) one or more phosphorous compounds selected from the group consisting of a phosphorus-containing carboxylic acid, a phosphorus-containing carboxylic acid ester, an acidic phosphoric acid ester, an amine salt of an acidic phosphoric acid ester, a phosphorous acid ester, a phosphorothionate, a thiophosphoric acid ester, a thiophosphoric acid metal salt, a thiocarbamic acid ester, and a thiocarbamic acid metal salt.
 30. The method of claim 29, wherein the phosphorus-containing carboxylic acid is a β-phosphorylated propionic acid, the phosphorus-containing carboxylic acid ester is a β-dithiophosphorylated propionic acid ester, the thiophosphoric acid metal salt is a zinc dialkyldithiophosphate or a molybdenum dialkyldithiophosphate, and the thiocarbamic acid metal salt is a zinc dithiocarbamate or a molybdenum dithiocarbamate.
 31. The method of claim 30, wherein the one or more phosphorous compounds are at a combined concentration that is in a range of 0.01 to 2 weight % of the base oil.
 32. The method of claim 31, wherein the lubricating oil composition further comprises one or more of the following: (d) one or more antioxidants at a combined concentration that is a range of 0.01 to 5 weight % of the base oil; (e) one or more metal deactivators at a combined concentration that is in a range of 0.01 to 0.5 weight % of the base oil; (f) one or more polyhydric alcohol fatty acid esters; (g) one or more pour-point depressants at a combined concentration that is in a range of 0.01 to 5 weight % of the base oil; (h) one or more viscosity index improving agents at a combined concentration that is in a range of 0.05 to 20 weight % of the base oil; (i) one or more anti-foaming agents at a combined concentration that is in a range of 0.0001 to 0.1 weight % of the base oil; and (j) one or more anti-emulsifiers at a combined concentration that is in the range of 0.005 to 0.5 weight % of the base oil. 